The present invention relates to a method of producing carboxylic acid esters of alcohols containing six or more carbon atoms by first preparing the methyl or ethyl ester and then transesterifying with the desired higher alcohol.
Specific esters of many substituted 2-pyridinyloxyalkanoic acids are conveniently prepared by the alkylation of salts of substituted 2-pyridinols with the corresponding ester of a haloalkanoic acid. For example, specific esters of (4-amino-3,5-dichloro-6--fluoro-2-pyridinyloxy)acetic acid are generally produced by alkylation of an alkali metal 4-amino-3,5--dichloro-6-fluoro-2-pyridinate with the corresponding ester of chloroacetic or bromoacetic acid as disclosed in U.S. Pat. Nos. 3,755,339; 4,542,221; and U.S. Pat. No. 4,701,531. A dipolar, aprotic solvent is sometimes employed. This method, while operable, has the disadvantage when applied to many esters of alcohols other than methanol and ethanol, of producing a product which is difficult to recover from the reaction medium in pure form. As a result, the desired ester products are often obtained in an unsatisfactory yield or with an unsatisfactory purity.
The higher esters of carboxylic acids, such as substituted 2-pyridinyloxyacetic acids including (4-amino-3,5-dichloro-6-fluoro-2-pyridinyloxy)acetic acid, on the other hand, are often more valuable than methyl or ethyl esters. This is because they are less volatile and those that are herbicidal are, in some situations, more effective or more selective in their action.